Energy scaling and extended tunability of a ring cavity terahertz parametric oscillator based on KTiOPO_(4) crystal

A wide terahertz tuning range from 0.96 THz to 7.01 THz has been demonstrated based on ring-cavity THz wave parametric oscillator with a KTiOPO_(4)(KTP)crystal.The tuning range was observed intermittently from 0.96 THz to 1.87 THz,from 3.04 THz to 3.33 THz,from 4.17 THz to 4.48 THz,from 4.78 THz to 4.97 THz,from 5.125 THz to 5.168 THz,from5.44 THz to 5.97 THz,and from 6.74 THz to 7.01 THz.The dual-Stokes wavelengths resonance phenomena were observed in some certain tuning angle ranges.Through the theoretical analysis of the dispersion curve of the KTP crystal,the intermittent THz wave tuning range and dual-wavelength Stokes waves operation during angle tuning process were explained.The theoretical analysis was in good agreement with the experiment results.The maximum THz output voltage detected by Golay cell was 1.7 V at 5.7 THz under the pump energy of 210 mJ,corresponding to the THz wave output energy of5.47μJ and conversion efficiency of 2.6×10^(-5).

Monochromatic and Tunable Terahertz Source Based on Nonlinear Optics

Recent progresses made by authors on monochromatic and tunable terahertz （THz） generation based on nonlinear optics are reviewed, including THz parametric oscillation （TPO） and difference frequency generation （DFG）. From the technical point of view, we develop extra- and intra-cavity surface-emitted TPO, as well as DFG with QPM-GaAs crystal. From the point of view of mechanism, Cherenkov phase-matching is comprehensively investigated in both bulk crystal and planar waveguide. A novel scheme for cascading enhanced Cherenkov DFG in waveguide is proposed. From the point of view of material, organic crystal 4-N,N-dimethylamino-4＇-N＇-methyl-stibazolium tosylate （DAST） is utilized as the nonlinear medium.

TTA Special Section on Terahertz Sources and Devices

Studies on terahertz（THz）radiation and functiona devices have drawn increasing attention due to their applications in biological imaging and sensing nondestructive evaluation,national security,spectroscopy and high speed communication.Tunable THz sources based on difference frequency or parametric oscillation generation are highly efficient and reliable for these applications

Optically pumped terahertz sources

High-power terahertz(THz) generation in the frequency range of 0.1-10 THz has been a fast-developing research area ever since the beginning of the THz boom two decades ago, enabling new technological breakthroughs in spectroscopy, communication, imaging,etc. By using optical(laser) pumping methods with near-or mid-infrared(IR) lasers, flexible and practical THz sources covering the whole THz range can be realized to overcome the shortage of electronic THz sources and now they are playing important roles in THz science and technology. This paper overviews various optically pumped THz sources, including femtosecond laser based ultrafast broadband THz generation, monochromatic widely tunable THz generation, single-mode on-chip THz source from photomixing, and the traditional powerful THz gas lasers. Full descriptions from basic principles to the latest progress are presented and their advantages and disadvantages are discussed as well. It is expected that this review gives a comprehensive reference to researchers in this area and additionally helps newcomers to quickly gain understanding of optically pumped THz sources.

Prospects of a β-SiC based IMPATT oscillator for application in THz communication and growth of aβ-SiC p-n junction on a Ge modified Si〈100〉substrate to realize THz IMPATTs

The prospects ofa p＋nn＋ cubic silicon carbide （3C-SiC/fl-SiC） based IMPATT diode as a potential solidstate terahertz source is studied for the first time through a modified generalized simulation scheme. The simulation predicts that the device is capable of generating an RF power output of 63.0 W at 0.33 THz with an efficiency of 13%. The effects of parasitic series resistance on the device performance and exploitable RF power level are further simulated. The studies clearly establish the potential of 3C-SiC as a base semiconductor material for a high-power THz IMPATT device. Based on the simulation results, an attempt has been made to fabricate β-SiC based IMPATT devices in the THz region. Single crystalline, epitaxial 3C-SiC films are deposited on silicon （Si） （100） substrates by rapid thermal chemical vapour deposition （RTPCVD） at a temperature as low as 800 ℃ using a single precursor methylsilane, which contains Si and C atoms in the same molecule. No initial surface carbonization step is required in this method. A p-n junction with an n-type doping concentration of 4 × 10^24 m-3 （which is similar to the simulated design data） has been grown successfully and the characterization of the grown 3C-SiC film is reported in this paper. It is found that the inclusion of Ge improves the crystal quality and reduces the surface roughness.

22 nm In0.75Ga0.25As channel-based HEMTs on InP/GaAs substrates for future THz applications

In this work,the performance of Lg = 22 nm In（0.75）Ga（0.25）As channel-based high electron mobility transistor（HEMT） on InP substrate is compared with metamorphic high electron mobility transistor（MHEMT） on GaAs substrate.The devices features heavily doped In（0.6）Ga（0.4）As source/drain（S/D） regions,Si double δ-doping planar sheets on either side of the In（0.75）Ga（0.25） As channel layer to enhance the transconductance,and buried Pt metal gate technology for reducing short channel effects.The TCAD simulation results show that the InP HEMT performance is superior to GaAs MHEMT in terms of fT,f（max） and transconductance（g（mmax））.The 22 nm InP HEMT shows an fT of 733 GHz and an f（max） of 1340 GHz where as in GaAs MHEMT it is 644 GHz and 924 GHz,respectively.InGaAs channel-based HEMTs on InP/GaAs substrates are suitable for future sub-millimeter and millimeter wave applications.